Filter vial

ABSTRACT

A filter vial and piston are provided where the vial has a cylindrical wall with a closed bottom and open top and with the hollow, tubular piston therein. The piston has a distal end covered by a cup having a proximal cup seal extending outward to engage the walls of the vial to form a fluid tight seal with the vial during use. The distal end of the piston has a piston flange extending outwardly and located adjacent a recess in the piston so the cup forms a snap fit over the piston flange and extends into the recess. The piston flange causes the cup to bulge sufficiently outward to form a fluid tight seal with the vial during use. A filter is placed in the bottom of the cup and abuts an inwardly extending lip on the cup. The filter is held against the lip by a piston support at the distal end of the piston. A cup support at a distal end of the cup also helps support the filter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of patent application No. 12/053,241filed Mar. 21, 2008 now U.S. Pat. No. 7,790,117.

STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT

Not Applicable

BACKGROUND

Filter vials have a tubular piston with a filter at the distal end ofthe piston. The piston fits into a mating vial containing a fluid andthings suspended in the fluid. When the piston is inserted into the vialfluid passes through the filter and into the piston in order to separatethe fluid from particles or molecules too large to pass through thefilter in the bottom of the piston. The filtered fluid can be extractedfrom the piston for further use.

The diameter and thickness of the filters can vary greatly from filterto filter and the thickness of the filter can vary greatly even acrossone filter. These variations make it difficult to seal the filters soall the fluid being filtered passes through the filter, and so thatfluid does not wick around the peripheral edge of the filter tocontaminate the filtered fluid in the piston. Further, as fluid isforced through the filters the filters can bow or otherwise deform andallow fluid to bypass the filter as it enters the body of the piston.Current assemblies use ultrasonically welded assemblies. Even if thefilters are ultrasonically welded to the adjacent walls that leavesplasticizers that contaminate the fluids placed in the vials during use.

BRIEF SUMMARY

A filter vial and piston are provided that has a cup which holds afilter in position on the piston during use so that all the fluid passesthrough the filter and none passes around the edges of the filter. Theparts are integrally molded so there is no contamination from ultrasonicwelding. The parts snap-fit together, but appropriates seals areprovided to prevent wicking or leakage at the location of thesnap-locks.

The filter vial assembly has a longitudinal axis along which the pistonmoves during use. The assembly includes a tubular vial having a closedbottom and an open top with walls defining a cylindrical interior havinga diameter D. A tubular piston is provided having opposing distal andproximal ends with at least the distal end being open. The piston haswalls defining a cylindrical interior with an exterior facing recessedportion adjacent the distal end the piston. The piston further has adistal piston flange at or adjacent to the distal end of the piston andextending outward from piston. A filter support is located inside thepiston at the distal end of the piston. A retainer cup is provided,having a sidewall extending between a proximal and distal ends of thecup with an interior diameter smaller than the distal seal on thepiston. The cup has a lip extending inward toward the longitudinal axisat the distal end of the retainer cup, and further has a cup sealextending outward from the proximal end of the cup a distance greaterthan the diameter D. The sidewall of the cup are sufficiently flexibleto deform outward as the cup passes over the distal seal on the pistonso the sidewalls assume an outer dimension larger than diameter D at thelocation of the piston flange when the retainer cup passes over thepiston distal seal. A filter is interposed between the retaining cup'slip and the distal end of the piston when the proximal end of theretainer cup is placed over the distal end of the piston.

The piston and retainer cup are placed through the open end of thefilter vial so the filter cup abuts and forms a fluid seal with theinside of the vial at the location of the cup seal and at the locationof the distal piston flange. Preferably, the recessed area extendsentirely around a circumference of the piston. Further, while the lippreferably extends continuously around an inner circumference of theretainer cup, it could be intermittent. The piston, vial and retainingcup are made of plastic, and preferably each part is separately formed.As desired, a cap is provided where the cap is sized to releasably butsnugly fit over the proximal end of the piston. Such caps are commonlyused, and typically have a flexible membrane through which a needle canbe inserted to withdraw filter fluid from inside the piston.Advantageously, but optionally, the proximal cup seal abuts an end ofthe recess in the piston during use. Preferably, there is an additionalseal extending outward from the piston adjacent the proximal end of thepiston and located to engage and form a fluid tight seal against thevial when the distal end of the piston is adjacent the bottom of thevial. Ideally, the piston flange has a generally triangular crosssectional shape which is larger at the proximal end and smaller at thedistal end of the seal.

There is also provided a method of forming a piston for a filter vial,where the piston has a cylindrical tube with opposing proximal anddistal ends. The method includes forming an outwardly extending pistonflange at the distal end of the piston. A cylindrical recess is formedaround a periphery of the distal end of the piston at the distal end ofthe piston and adjacent to the piston flange and on the proximal side ofthe piston flange. A filter is placed in the bottom of a retaining cupwhich cup is sized to fit over the distal end of the piston. Theretaining cup is provided with an open proximal end and an inwardextending lip at an opposing distal end which lip abuts a periphery ofthe filter. The method also includes placing the open proximal end ofthe cup over the distal end of the piston and piston flange to form asnap fit between the proximal end of the cup and the recess on thepiston and advancing the retaining cup along the piston until the distalend of the piston abuts the filter. The retaining cup is provided withan outwardly extending seal at the proximal end sized to sealinglyengage the inside of the filter vial during use. The retaining cup ismade of sufficiently flexible material to bulge outward at the pistonflange with the piston flange and retaining cup being dimensioned toextend outward a distance sufficient to form a fluid tight seal withwalls of the filter vial during use.

In further variations, the method includes providing a filter support onthe distal end of the retaining cup, the cup filter support located toabut the filter during use. The method can also include providing apiston filter support on the distal end of the piston, with the pistonfilter support located to abut the filter during use. Advantageously,the method also includes providing a piston filter support on the distalend of the piston, the piston filter support located to abut the filterduring use. Finally, the method includes placing a rib on a distal edgeof the piston located to form an axial facing seal around a periphery ofthe filter.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the various embodimentsdisclosed herein will be better understood with respect to the followingdescription and drawings, in which like numbers refer to like partsthroughout, and in which:

FIG. 1 is an exploded side view of a piston, retainer and vial;

FIG. 2 is a sectional view of FIG. 1;

FIG. 3 is a cross-sectional view of the piston and retainer in anassembled configuration;

FIG. 4 is a cross-sectional view of the piston, retainer and vial in anassembled configuration with the piston partially inserted into thevial;

FIG. 5 is an end view of the retainer cup of FIG. 1, looking from thedistal end toward the proximal end;

FIG. 6 is an end view of the piston of FIG. 1, looking from the distalend toward the proximal end;

DETAILED DESCRIPTION

Referring to FIGS. 1-4, a tubular piston 10 with a circularcross-section has proximal and distal ends 12, 14, respectively, with aporous piston support 16 located at the distal end 14. The support 16advantageously takes the form of radial arms intersecting at a centrallocation on the longitudinal axis 18 of the piston 10. The terms distaland proximal refer to relative locations of parts along the longitudinalaxis 18, and the terms inward and outward refer to relative directionstoward and away from the longitudinal axis 18. One or more flanges 20extend radially from the proximal end 12. A first, proximal seal 22 islocated adjacent to but inward from the proximal end 12 and extendsoutward, away from longitudinal axis 18. A vent hole 24 is adjacent theseal 22 but located slightly toward the distal end 14. Adjacent to andpreferably extending to the distal end 14 is a recessed area 26 having asmaller diameter than that of the body of piston 10 forming a shoulder27 at the location of the larger diameter portion of the piston body. Anoutward extending distal piston flange 28 is located adjacent the distalend 14 in this recessed area. An axially extending tip 31 (FIG. 2) ispreferably, but optionally provided that encircles the distal end of thepiston 10. The tip 31 preferably has a triangular cross section and isvery small.

A retainer cup 30 has an inner diameter sized to fit snugly against thepiston recess 26. The retainer cup 30 has proximal and distal ends 32,34, respectively, with a porous cup support 36 over the distal end 34and a third, cup seal 38 at the proximal end, extending outward, awayfrom the axis 18. The support 36 is like the support 16. A membranefilter 40 fits inside the retainer cup 30 and abuts the cup support 36.The membrane filter 40 is disc shaped, usually with an axial thicknessthat is several times smaller than its diameter. In some situationsmultiple filters 40 can be stacked. An inward extending lip 41 at thedistal end 34 of the cup 30 provides an axial support around theperiphery of the filter 40. The tip 31 (FIG. 2) on the distal end of thepiston 10 presses the filter 40 against this lip 41 when the parts areassembled.

The supports 16, 36 preferably take the form of radial struts or spokesextending from the walls of piston 10 or cup 30, respectively. But thesupports 16, 36 could take other forms, such a rectangular or squaregrid work, or a plate with drain holes therein. A spoke with atriangular cross-section is believed suitable, with the apex of thetriangle abutting the filter 40 in order to reduce blockage of thefilter. Since supports 16, 36 abut opposing sides of the filter 40, aspoke with a triangular cross section will require orientating theapexes so they are toward each other. While four spokes are shown, sixequally spaced spokes are believed preferable. Too many spokes blockflow through the filter 40, and too few spokes allow the filter to flexand allow unfiltered fluid to bypass the filter by flowing around theperiphery of the filter. The intersection of the spokes at the center ispreferably small so as not to block fluid flow through the filter, witha center obstruction of about 0.1 inches for a piston 10 with an innerdiameter of about 0.3 inches. The dimensions will vary with the sizesand with the strength of the materials used.

A tubular vial 42 has an open proximal end 44 and a closed distal end46. The vial 42 is sized and shaped so the retainer cup 30 and piston 10fit within the vial. The vial 42, cup 30 and piston 10 are preferablyall cylindrical with a circular cross section, but other shapes could beused.

Referring to FIG. 3, the retaining cup 30 fits over piston flange 28 andabuts the recessed portion 26 on distal end 14 of piston 10 so thepiston support 16 abuts membrane filter 40 and preferably presses thefilter 40 against lip 41 and against cup support 36. Ideally thecircular tip 31 provides a concentrated force around the periphery ofthe filter 40 to clamp the filter against the lip. The filter 40 is thusheld in position by the lip 41 and tip 31, and further supported by thesupports 16, 36. The tip 31 and lip 41 hold the periphery of the filter40 in position with the tip 31 providing an axial compression sealagainst the filter 40. Movement, such as bowing or twisting of the bodyof the filter 40, is restrained by the supports 16, 36. The combinationof supports 16, 36, lip 41 and tip 31 are sufficient so that the sealbetween the periphery of the filter 40 and lip 41 does not leak asfiltrate fluid 50 is forced through the filter 40.

As the retainer cup 30 fits over the recessed portion 26, the flange 28forces the sidewall 29 of the cup 30 outward to form a fluid tight sealand the proximal end 32 preferably abuts or comes close to shoulder 27.The piston flange 28 is preferably at or very close to the distal end 14of piston 10, and is interposed between the outer wall of piston 10 andthe inner wall of the cup 30 to form a fluid tight seal. Advantageously,the piston support 16 presses the filter 40 against the lip 41 enough toprevent any leakage past the end of the filter 30, and preferably thefilter is compressed by the circular periphery of distal end 14 ofpiston 10, or compressed by the circular periphery of the support 16, sothat any fluid wicking between the outer periphery of the filter 10 andthe wall 29 of the cup 30, does not enter the cup. The location of theshoulder 27 and the axial length of the sidewall 29 of cup 30 can beselected to achieve a desired amount of compression.

As the retainer cup 30 fits over the recessed portion 26 and the seal26, the sidewall 29 of the cup 30 is deformed outward so the outerdiameter of the assembled cup 30 and piston 10 is slightly larger thanthe diameter of the piston body 10. The assembled cup 30 and piston 10are then fit into vial 42 to force fluid or filtrate 50 through thefilter 40 and into the hollow interior of the tubular piston 10.Preferably, but optionally, the piston flange 28 bulges the sidewall 29of cup 30 outward enough to form a fluid tight seal with the inner wallsof vial 42. The seal 38 is also sized relative to the inner walls ofvial 42 to form a fluid tight seal with the vial. Advantageously, thereare thus two outward facing seals adjacent the distal end 14 of thepiston 10 which seal against the interior walls of vial 42.

As the piston is advanced along longitudinal axis 18, fluid or filtrate50 passes though filter 40 and into the body of piston 10, with airescaping through vent 24. Eventually the seal 22 enters the vial 42 andalso seals against the inner walls of vial 42. Filtrate 50 passingthrough the filter 40 is in the hollow body of piston 10 where it can beremoved directly, or through an opening in cap 52 which is fitted overthe proximal end 12 of the piston 10. Materials entrained in thefiltrate 50 which are too large to fit through the filter 40 areretained between the filter 40 and the closed distal end 46 of the vial.Preferably the cap 52 forms a snap fit with the proximal end of thepiston 10, and more preferably has an inwardly extending rim or lip thatforms a snap-fit over flange(s) 20 on the piston 10.

The amount of deformation or bulging caused by forcing the cup 30 overthe flange 28 affects the quality of the fluid tight seal formed betweenthe sidewall 29 of the cup 30 and the inner wall of vial 42 at thelocation of the flange 28. The deformation is affected mostly by thestiffness of the sidewall 29 on cup 30, the thickness of the wall on cup30, the stiffness of the flange 28, the shape and size of the flange 28.Further, the flange 28 is stiff enough that it does not loose itscircular shape and forms a fluid tight seal around the entirecircumference of the abutting inner side of sidewall 29 of cup 30. InFIG. 4, the walls of the vial 42 are shown as slightly deforming at thetwo seal locations, but such deformation is optional and will vary withthe thickness and material used for the vial 42. Advantageously theflange 28 has an inclined surface angled outward and inclining from thedistal toward the proximal end of the piston.

The seal 38 also preferably has an inclined surface angled outward andinclining from the distal toward the proximal end of the piston. Theseal 22 also preferably has an inclined surface angled outward andinclining from the distal toward the proximal end of the piston.

The seals 22, 28 and flange 38 preferably have a generally triangularcross-section, and are integrally molded with the piston 10, or cup 30.This construction allows the walls of piston 10 and vial 42 to be thinwhile the seals 22, 28 and flange 38 are strong and maintain theircircular shape and sealing uniformity during use. Differentcross-sectional shapes could be used. Likewise, the supports 16, 36 areintegrally molded during formation of the piston 10 and cup 30,respectively.

The plug inserted into the hollow body of piston 10 and the hollow cupportion of cup 30 passes along the longitudinal axis 18. If the supports16, 36 each have a triangular cross-section with the apexes of thetriangles facing opposing sides of the filter 40 during use, then amating plug must be used to form the distal end of the piston 10 to formthe triangular cross-section of the supports. Alternatively, thecross-section of the struts could be generally square or rectangular nwhich case the reverse shapes could be formed in the molding plug withonly sufficient taper to allow withdrawal of the plug after molding. Theformation of supports 36 with a triangular cross section on the cup isnot difficult as the triangular shape can be formed in the end of themolding plug and the angles facilitate withdrawal of the plug.

Other seal types could also be used for seals 28, 22, 38, but arebelieved much less desirable. For example, O-ring seals set inrectangular or semi-circular recesses could be used. But the recessesused to position such seals reduce the wall thickness and strength ofthe walls, making them undesirable. Thus, the seals 28, 22, 38 arepreferably integrally molded or cast with the parts from which theyextend. Further, the preferred piston 10, cup 30 and vial 42 are moldedout of various plastics and that makes forming suitable recesses to holdthe O-ring or even D-ring seals difficult because the recesses reducethe strength of the parts.

The piston 10, cup 30 and vial 42 are preferably molded of a suitableplastic, preferably one that does not contaminate samples placed in thevial 42. The vial is preferably made of polyolefin, preferablypolypropylene, or other suitable polymer. The filter 40 is preferably,but optionally made of Teflon, nylon, glass fiber or other filtermaterials such as PVDF (polyvinyldifloride) or PES (polyethersulphone),etc.

In use, the filter 40 is placed inside the retaining cup 30. The cup 30is then snap fit over piston flange 28 and onto the distal end of thepiston 10, and preferably (but optionally) pushed along the piston untilthe cup seal 38 abuts the shoulder 27 on the piston. At this point thefilter 40 is held between the distal end of the piston 10 and lip 41,and preferably held between the piston support 16 and cup support 36 andlip 41. The tip 31 pressing the filter 40 against lip 41 advantageouslyforms an axial seal encircling the filter 40 near the periphery of thefilter, and further helps prevent the periphery of the filter fromdeforming between the spaces in the supports 16, 36 and thus helpsprovide a good seal at the periphery of the filter. The supports 16, 36prevent the filter 40 from bending along axis 18 and breaking the sealat the periphery of the filter.

The tip 31 preferably has a triangular cross-section with the apexabutting the filter 40. During assembly, the tip 31 is preferably smallenough that it deforms when it presses the filter 40 against the lip 41.A tip 31 having a height of about 0.01 inches is believed suitable whenused on a piston 10 with an inner diameter of about 0.3 inches so thediameter of the tip 31 is slightly smaller. The tip 31 may be viewed asa rib on the circular distal edge of the tubular piston 10.

This assembly also forms two outwardly extending portions, one at thelocation where the piston flange 28 forces the sidewall 29 of cup 30outward, and the other at the location of cup seal 38. Both of theseseal locations are larger than the inside of tubular vial 42 and formtwo seals with the vial. Both of these seal locations are preferablyseparated by a distance sufficient that the wall of the vial 42 extendsinward toward longitudinal axis 18 a slight distance in order to ensurea good fluid-tight seal at both locations.

As seen in FIGS. 1-2, the distal piston flange 28 is located slightlybefore the end of the piston 10, so that there is a short cylindricalsection before the inclined flange 28 begins. This cylindrical sectionis optional. This cylindrical section could be formed by ultrasonicallywelding a disc-shaped filter support 16 (piston support 16) having acylindrical periphery onto the distal edge of the piston 10. But suchultrasonic welding leaves contaminants, as do adhesives. Thus, thefilter support 16 is preferably integrally molded simultaneously withthe formation of the piston 10 and thus made of the same material as thepiston 10. This integral molding is usually difficult because of thelength of the piston 10 is typically several times longer than thediameters of the piston so it is difficult to mold interior parts.

The piston flange 28, and to a lesser extent the flange 28 and recess26, thus forms a snap lock to hold the retaining cup 30 onto the end ofthe piston 10. But the flange 28 also cooperates with the deformablewall 29 of the retainer cup 30 to bulge the sidewall 29 outward and forma sealing location at the distal end of the cup 30 and at the distal endof the piston 10.

A fill line 54 is optionally placed on the outside of the vial 42 toindicate a maximum level of fluid placed inside the vial. The walls ofthe vial are preferably sufficiently transparent or translucent so theplacement of fluid inside the vial 42 can be seen from outside the vialto allow use of the fill line 54. The fill line 54 can be molded intothe vial as an outwardly extending flange or inwardly extending recess,or the fill line can be marked by paint, marker, abrasion, laseretching, chemical etching, or other process leaving a visible indicia.

The distal end 14 of the piston 10 could hold the filter against theinwardly extending lip 41 on the cup. But preferably one, and optimallyboth supports 16, 36 are also used to hold the filter in place and tosupport the middle of the filter during use. The piston support 16restrains the filter from bowing and leaking around the periphery as thepiston advances into the vial and fluid is forced through the filter.The piston support 16 is thus preferably stronger than the cup support36. The piston 10 can be made of an equal or stronger and hardermaterial than the retaining cup 30, especially since the retaining cup30 must have a sidewall 29 flexible enough to slide over the pistonflange 28 and form a snap fit with the piston recess 26. Preferably thepiston 10 is of the same material as the retaining cup 30, but the cupis slightly thinner and thus more flexible,

The above description is given by way of example, and not limitation.Given the above disclosure, one skilled in the art could devisevariations that are within the scope and spirit of the inventiondisclosed herein, including various ways of shaping the seals 28, 38.Further, the various features of the embodiments disclosed herein can beused alone, or in varying combinations with each other and are notintended to be limited to the specific combination described herein.Thus, the scope of the claims is not to be limited by the illustratedembodiments.

1. A filter vial kit, comprising: a tubular vial having longitudinalaxis, a closed bottom, an open top and a cylindrical interior wall witha diameter D joining the bottom; a tubular piston with opposing distaland proximal ends with at least the distal end being open, the pistonhaving a cylindrical wall with an exterior facing side of that wallhaving a recessed portion adjacent the distal end the piston, the pistonfurther having a distal piston flange at or adjacent to the distal endof the piston and extending outward from the piston; a filter support atthe distal end of the piston; a retainer cup having a bottom andcontinuous sidewall around the bottom with the sidewall extendingbetween a proximal and distal end of the cup, the cup sidewall having aninterior diameter smaller than the distal piston flange, the cup furtherhaving a cup seal extending outward from the proximal end of the cup adistance greater than the diameter D, the sidewall of the cup beingsufficiently flexible to deform outward as the cup passes over thedistal piston flange so the sidewall can have an outer dimension largerthan diameter D at the location of the piston flange when the retainercup passes over the distal piston flange; and a filter that isconfigured to fit between and be held between the retaining cup and thedistal end of the piston when the proximal end of the retainer cup isplaced over the distal end of the piston.
 2. The filter vial kit ofclaim 1, wherein the filter support is inside the piston.
 3. The filtervial kit of claim 1, wherein the cup has a lip extending inward towardthe longitudinal axis at the distal end of the retainer cup a distancesufficient to stop passage of the filter along the longitudinal axis. 4.The filter vial kit of claim 3, wherein the lip on the cup extendscontinuously around an inner circumference of the retainer cup and therecessed area extends entirely around a circumference of the piston. 5.The filter vial kit of claim 1, wherein the distal end of the piston hasa distal edge with a tip extending around a circumference of the pistonand further extending axially and located to press the filter againstthe lip of the cup during use.
 6. filter vial kit of claim 1, whereinthe piston, vial and retaining cup are made of a polymer.
 7. The filtervial kit of claim 1, further comprising a cap sized to releasably butsnugly fit over the proximal end of the piston.
 8. The filter vial kitof claim 2, wherein the sidewall of the cup between the proximal anddistal end of the cup is sized to allow the end of the cup seal on theproximal end of the cup to abut an end of the recess in the piston whenthe piston is forced against a filter in the bottom of the cup.
 9. Thefilter vial kit of claim 1, further comprising a seal extending outwardfrom the piston adjacent the proximal end of the piston and located toengage and form a fluid tight seal against the interior wall of the vialwhen the distal end of the piston is adjacent the bottom of the vial.10. The filter vial kit of claim 1, wherein the piston flange has agenerally triangular cross sectional shape.
 11. A piston for a filtervial assembly having a tubular filter vial with an open proximal end anda closed distal end and a cylindrical sidewall of diameter D,comprising: a tubular piston having a longitudinal axis, the pistonhaving a proximal end and a distal end with a porous bottom throughwhich fluid can flow during use, the piston having a piston flange atthe distal end which flange extends away from the longitudinal axis; aretaining cup having a proximal end and a distal end with a porousbottom through which fluid can flow during use, the cup having acontinuous sidewall overlapping the distal end of the piston and withthe sidewall being sufficiently flexible to deform around the pistonflange to achieve a diameter greater than D in a plane orthogonal to thelongitudinal axis and through the piston flange but small enough for thepiston to fit in the open end of the filter vial during use, the cuphaving a cup seal at a proximal end of the continuous wall; and a filterlocated between the distal end of the piston and the distal end of thecup.
 12. A method of sealing a tubular piston against an interiorcylindrical sidewall of a filter vial having a closed bottom joined tothe sidewall, the piston having a cylindrical tube with opposingproximal and distal ends and sized so the piston fits into the vial toforce fluid in the vial through a filter and also through one or moreopenings in the distal end of the piston and into an interior of thetubular piston as the piston advances along a longitudinal axis of thevial, comprising: placing a cup over the distal end of the piston, thedistal end of the piston having an outwardly extending piston flange andthe cup having a flexible cylindrical sidewall and a porous bottom withthe piston flange deforming the flexible cup sidewall outward; insertingthe piston flange and piston into the vial, the piston flange deformingthe flexible cup sidewall outward a distance sufficient to abut theinner periphery of the filter vial and form a first fluid seal betweenthe vial and cup sidewall at the location of the piston flange, the cuphaving a distal and proximal end with the bottom of the cup at thedistal end of the cup, the cup having a cup seal around the proximal endof the cup with the cup seal extending outward a distance sufficient tocontact the inner periphery of the filter vial, the cup seal beinglocated between the piston flange and the proximal end of the pistonwhen the cup is on the piston; and moving one of the piston or bottom ofthe vial toward the other until the cup seal enters the vial and forms asecond fluid seal around the inner periphery of the filter vial.
 13. Themethod of claim 12, further comprising, advancing the piston into thevial to force fluid in the vial into the interior of the piston.
 14. Themethod of claim 13, further comprising inserting a filter between thedistal end of the piston and the bottom of the cup with the cup andpiston each abutting the filter to hold it in a position where fluidfrom the vial passes through the filter to go inside the piston.
 15. Themethod of claim 13, wherein the filter vial has a sufficiently flexiblesidewall that at least one of the first and second seals deforms thevial sidewall outward.
 16. The method of claim 13, wherein the cup andvial each have flat bottoms.
 17. A filter vial and piston, the filtervial having a cylindrical sidewall and a closed bottom to hold a fluidtherein, the piston having a tubular portion with an end and a filterover that end through which the fluid passes to go inside the piston asthe piston advances along a longitudinal axis of the vial, furthercomprising: a piston flange at the end of the piston by the filter, thepiston flange extending away from the longitudinal axis and completelyaround an outer periphery of the piston; a flexible cup having acontinuous, cylindrical sidewall and a porous bottom in an undeformedconfiguration, the cup having a cup seal spaced away from the bottomalong the longitudinal axis with the cup seal extending away from thelongitudinal axis, the cup configured to be placed over the porous endof the piston and piston flange during use with the cup sidewall beingsufficiently flexible to deform around the piston flange and therelative dimensions of the piston flange and cup sidewall beingconfigured to achieve such deformation during use; and wherein thesidewall of the filter vial is sufficiently smaller in diameter than thediameter of the sidewall of the cup when deformed by the piston flangeto form a fluid seal with the sidewall of the filter vial when thedeformed cup is moved along the longitudinal axis toward the closedbottom.
 18. The filter vial and piston of claim 17, further comprising afilter in the bottom of the flexible cup.
 19. The filter vial and pistonof claim 18, further comprising a portion of fluid interposed betweenthe filter and the closed end of the vial, wherein the piston isinserted into the cup with the piston flange deforming the sidewall ofthe cup and the deformed cup sidewall seals against the sidewall of thefilter the vial.
 20. The filter vial and piston of claim 18, furthercomprising a portion of a fluid sample being located between the filterand the closed end of the vial and a portion of the fluid sample on anopposing side of the filter, and wherein the piston is inserted into thecup with the piston flange deforming the sidewall of the cup and thedeformed cup sidewall seals against the sidewall of the filter the vial.